CLK/OSBindings/Mac/Clock Signal/Audio/CSAudioQueue.m

//
//  AudioQueue.m
//  Clock Signal
//
//  Created by Thomas Harte on 14/01/2016.
//  Copyright © 2016 Thomas Harte. All rights reserved.
//

#import "CSAudioQueue.h"
@import AudioToolbox;

#define AudioQueueBufferMaxLength		8192

@implementation CSAudioQueue
{
	AudioQueueRef _audioQueue;
}

#pragma mark - AudioQueue callbacks

- (void)audioQueue:(AudioQueueRef)theAudioQueue didCallbackWithBuffer:(AudioQueueBufferRef)buffer
{
	[self.delegate audioQueueDidCompleteBuffer:self];
	AudioQueueFreeBuffer(_audioQueue, buffer);
}

static void audioOutputCallback(
	void *inUserData,
	AudioQueueRef inAQ,
	AudioQueueBufferRef inBuffer)
{
	[(__bridge CSAudioQueue *)inUserData audioQueue:inAQ didCallbackWithBuffer:inBuffer];
}

#pragma mark - Standard object lifecycle

- (instancetype)initWithSamplingRate:(Float64)samplingRate
{
	self = [super init];

	if(self)
	{
		_samplingRate = samplingRate;

		// determine preferred buffer sizes
		_preferredBufferSize = AudioQueueBufferMaxLength;
		while((Float64)_preferredBufferSize*50.0 > samplingRate) _preferredBufferSize >>= 1;

		/*
			Describe a mono 16bit stream of the requested sampling rate
		*/
		AudioStreamBasicDescription outputDescription;

		outputDescription.mSampleRate = samplingRate;

		outputDescription.mFormatID = kAudioFormatLinearPCM;
		outputDescription.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger;

		outputDescription.mBytesPerPacket = 2;
		outputDescription.mFramesPerPacket = 1;
		outputDescription.mBytesPerFrame = 2;
		outputDescription.mChannelsPerFrame = 1;
		outputDescription.mBitsPerChannel = 16;

		outputDescription.mReserved = 0;

		// create an audio output queue along those lines
		if(!AudioQueueNewOutput(
				&outputDescription,
				audioOutputCallback,
				(__bridge void *)(self),
				NULL,
				kCFRunLoopCommonModes,
				0,
				&_audioQueue))
		{
			AudioQueueStart(_audioQueue, NULL);
		}
	}

	return self;
}

- (instancetype)init
{
	return [self initWithSamplingRate:[[self class] preferredSamplingRate]];
}

- (void)dealloc
{
	if(_audioQueue) AudioQueueDispose(_audioQueue, NO);
}

#pragma mark - Audio enqueuer

- (void)enqueueAudioBuffer:(const int16_t *)buffer numberOfSamples:(size_t)lengthInSamples
{
	AudioQueueBufferRef newBuffer;
	size_t bufferBytes = lengthInSamples * sizeof(int16_t);

	AudioQueueAllocateBuffer(_audioQueue, (UInt32)bufferBytes, &newBuffer);
	memcpy(newBuffer->mAudioData, buffer, bufferBytes);
	newBuffer->mAudioDataByteSize = (UInt32)bufferBytes;

	AudioQueueEnqueueBuffer(_audioQueue, newBuffer, 0, NULL);
}

#pragma mark - Sampling Rate getters

+ (AudioDeviceID)defaultOutputDevice
{
	AudioObjectPropertyAddress address;
	address.mSelector = kAudioHardwarePropertyDefaultOutputDevice;
	address.mScope = kAudioObjectPropertyScopeGlobal;
	address.mElement = kAudioObjectPropertyElementMaster;

	AudioDeviceID deviceID;
	UInt32 size = sizeof(AudioDeviceID);
	return AudioObjectGetPropertyData(kAudioObjectSystemObject, &address, sizeof(AudioObjectPropertyAddress), NULL, &size, &deviceID) ? 0 : deviceID;
}

+ (Float64)preferredSamplingRate
{
	AudioObjectPropertyAddress address;
	address.mSelector = kAudioDevicePropertyNominalSampleRate;
	address.mScope = kAudioObjectPropertyScopeGlobal;
	address.mElement = kAudioObjectPropertyElementMaster;

	Float64 samplingRate;
	UInt32 size = sizeof(Float64);
	return AudioObjectGetPropertyData([self defaultOutputDevice], &address, sizeof(AudioObjectPropertyAddress), NULL, &size, &samplingRate) ? 0.0 : samplingRate;
}

@end